1. Field of the Invention
The present invention relates to wireless IC devices. More particularly, the present invention relates to a wireless IC device capable of detecting an environmental state based on a state of a communication characteristic between the wireless IC device and an external reader apparatus. In addition, the present invention relates to a method of detecting an environmental state using the wireless IC device.
2. Description of the Related Art
In recent years, Radio Frequency Identification (RFID) technologies have been put into practical use and wireless IC devices having RFID integrated circuit (IC) chips mounted therein have been utilized for various individual identifications including merchandise control and employee ID cards.
Several methods are used for the RFID. For example, in wireless IC devices adopting passive methods, radio waves having certain frequencies transmitted from reader apparatuses (or reader-writer apparatuses) are received with antennas, RFID IC chips are driven by using the radio waves as power sources to extract information from the IC chips, the information is put on reflected waves from the wireless IC device to the reader apparatus, and the reflected waves including the information are transmitted to the reader apparatuses.
In addition, an approach has been made to use the RFID wireless IC devices for transmission of detection results in sensors that detect environmental states in recent years. For example, in a sensor system disclosed in Japanese Unexamined Patent Application Publication No. 2001-291181, a sensor detecting water leakage from pipes, a sensor detecting the humidity of the soil in a pot, or the like is combined with an RFID wireless IC device, radio waves from a reader apparatus are also used as a driving source for the sensor, the detection result in the sensor is put on reflected waves from the wireless IC device to the reader apparatus, and the reflected waves including the detection result in the sensor are transmitted to the reader apparatus.
However, since a minute change in an electrical characteristic based on a change in the environmental state is digitized and the data is transmitted by using communication components in the sensor system in related art disclosed in Japanese Unexamined Patent Application Publication No. 2001-291181, there is a problem in that the number of components is increased, which causes increases in cost and manufacturing complexity.